1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus, both employing an intermediate transfer-recording system. More particularly, the invention relates to an image forming method and an image forming apparatus, which are designed to form high-quality portraits for personal IDs, binary images (e.g., characters) or anti-forging images on media such as cards and brochure pages.
2. Description of the Related Art
Known as such an image forming method is the intermediate transfer-recording method. In this method, a thermal heat transfers ink from an ink ribbon to an intermediate transfer-recording medium, thus forming an image on the medium. This image is transferred from the medium to a final transfer-recording medium such as a card or a brochure page. In the intermediate transfer-recording method, any image is first formed on the intermediate transfer-recording medium having an image-receiving layer, unlike in the method that forms an image directly on the final recording medium. Therefore, the intermediate transfer-recording method can form a stable image, regardless of the condition of the transfer-recording surface of the final recording medium.
In the thermal transfer recording system using a thermal head, dust, for example, may exist between the image-receiving layer of the intermediate transfer-recording medium and the ink ribbon or between the thermal head and the ink ribbon. In this case, some color dots cannot be transferred to the recording medium, inevitably forming an image having no desired color.
After transferred to the final recording medium, such an image is visually examined for defects. If the image has defects that are too prominent, the final recording medium is discarded, and the same image is transferred from the intermediate transfer-recording medium to a new final recording medium such as a card or a brochure page. In recent years, various sophisticated measures have been taken to prevent forgery on the final recording media thus discarded, such as cards and brochure pages. Further, relatively expensive final recording media have come into use in increasing numbers, each incorporating an IC chips, typically a radio IC chip. In view of these facts, the discarding of the cards and brochure pages, because of the above-mentioned defective images, makes a great economic loss.
A technique is known, which may avoid such an economic loss (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-283598). This technique is to compare an image formed on an intermediate transfer-recording medium with the original image represented by image data, before the image transferred to a final recording medium, determining whether the image is defective or not. In accordance with whether the image is defective, it is then determined whether the image should be transferred to the final recording medium.
The technique can prevent an image from being transferred to a final recording medium if the image has been found to be defective. Hence, final recording media will not be wasted, thus avoiding the above-mentioned economic loss.
However, the accuracy of determining whether an image is defective is low. This is because the image formed on an intermediate transfer-recording medium is compared with only the original image represented by image data, and the amount of data used in determining the defectiveness of the image is inevitably too small.
The technique described above uses an inspection algorithm. The algorithm is so described that an image, such as a person's portrait, for example, is inspected in accordance with the contour of the face or the binary-image area thereof. It is therefore difficult to detect defects in the pixels that constitute the image. The algorithm cannot help to accomplish the inspection at a desirable precision.